Skin flaps were elevated on the backs of guinea pigs. Flaps elevated without a previous delay procedure exhibited necrosis of the distal third of the flap. A preceding delay procedure followed after 1 to 2 weeks by flap elevation improved flap survival. Microanalytical methods were utilized to quantitate the local tissue metabolic alterations occurring in delayed and undelayed skin flaps by analyzing some of the key enzymes in each pathway of glucose metabolism. The distal extremity of undelayed flaps exhibited an abrupt decrease in glucose concentration in the epidermis and the superficial layers of the dermis. The distal third of the delayed bipedicle flaps exhibited little alteration in tissue flucose content throughout a 3 week period following delay. Comparison of representative enzyme activities between undelayed and delayed flaps suggested that the mechanism of delay might consist of a metabolic adaptation of flap tissue to partial ischemia. This adaptation is characterized by increased activities of glycolysis and the pentose phosphate pathway. Further study will include assays of enzyme activities and overall rates of carbohydrate, amino acid, and nucleic acid metabolism in undelayed and delayed skin flaps and free flaps. The responses of each tissue component of skin flaps will be characterized by quantitative histochemical studies.